Let ob = oc = OA = R.

∫ arc AC= arc BC, and AB is the diameter.

∴CO⊥AB？ And MF⊥CO of ME⊥AB.

∴ rectangular MFOE? That is MF=OE.

∴MF=OEE

∵MF⊥CO BO⊥CO

∴MF∥OB？ That is ∠CMF=∠CBO.

∵RT isosceles △COB

∴∠CMF=∠CBO=45

∴RT isosceles △CFM

∴CF=FM=√(CM？ /2)= 1

∴FM=OE= 1

∵ isosceles △MAD

∴AE=ED=OE+AO= 1+r

∫BD = ED-BE？ And BE=OB-OE=r- 1.

∴bd= 1+r-r+ 1=2